Distribution and characterization of ampicillin- and tetracycline-resistant <Emphasis Type="Italic">Escherichia coli</Emphasis>from feedlot cattle fed subtherapeutic antimicrobials |
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Authors: | Parasto Mirzaagha Marie Louie Ranjana Sharma L Jay Yanke Ed Topp Tim A McAllister |
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Institution: | (1) Agriculture and Agri-Food Canada, Lethbridge Research Centre, Lethbridge, Alberta, T1J 4B1, Canada;(2) Faculty of Medicine, University of Calgary, Calgary, Alberta, T2N 4N1, Canada;(3) Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, London, Ontario, N5V 4T3, Canada |
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Abstract: | Background Feedlot cattle in North America are routinely fed subtherapeutic levels of antimicrobials to prevent disease and improve the
efficiency of growth. This practice has been shown to promote antimicrobial resistance (AMR) in subpopulations of intestinal
microflora including Escherichia coli. To date, studies of AMR in feedlot production settings have rarely employed selective isolation, therefore yielding too
few AMR isolates to enable characterization of the emergence and nature of AMR in E. coli as an indicator bacterium. E. coli isolates (n = 531) were recovered from 140 cattle that were housed (10 animals/pen) in 14 pens and received no dietary antimicrobials
(control - 5 pens, CON), or were intermittently administered subtherapeutic levels of chlortetracycline (5 pens-T), chlortetracycline
+ sulfamethazine (4 pens-TS), or virginiamycin (5 pens-V) for two separate periods over a 9-month feeding period. Phenotype
and genotype of the isolates were determined by susceptibility testing and pulsed field gel electrophoresis and distribution
of characterized isolates among housed cattle reported. It was hypothesized that the feeding of subtherapeutic antibiotics
would increase the isolation of distinct genotypes of AMR E. coli from cattle. |
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